A rope traction device is a type of winding instrument used for construction, loading and unloading and conveying machines such as moving scaffolds, elevators and cranes and is capable of moving up and down along a rope with the rope wound around its sheave by only one or a few windings and without winding the rope around and feeding it from a drum.
An example of a prior art rope traction device used for moving up and down a moving scaffold for performing work along an exterior wall surface of a building is shown in FIGS. 3 and 4. This rope traction device includes a frame 1, a drive shaft 2 mounted on the frame 1, a motor 3 provided on the outer periphery of the drive shaft 2 through a bearing and a sheave 4 driven by this motor 3. The rope traction device further includes a traction mechanism 6 for holding a rope 5 wound about this sheave 4 by one winding for preventing the rope 5 from slipping off the sheave 4 and further a brake mechanism 7.
This traction mechanism 6 includes an L-shaped pivoting arm 8 provided in the vicinity of a point at which the rope 5 is disengaged from the sheave 4. A pair of rollers 9, 9 are rotatably mounted at one end of the pivoting arm 8 to press the rope 5 inwardly from a straightly tightened state thereof. Another pair of rollers 10, 10 are rotatably mounted on a pivoting arm 11 which is pivotably mounted at the other end of the pivoting arm 8.
According to this structure, as the rope 5 becomes straightly tightened, the rollers 9, 9 which are in contact with the rope 5 are pushed by the rope outwardly and the pivoting arm 8 thereby is pivoted in a counterclockwise direction to cause the rope 5 to be pressed by the rollers 10, 10 to the groove of the sheave 5.
The output shaft of the motor 3 is coupled to the drive shaft 2 and a wheel 14 of an intermediate shaft 13 is meshed with a pinion 12 provided on the drive shaft 2. A second pinion 15 of the intermediate shaft 13 is meshed with a gear 20 of a brake wheel 19 having a female screw 18 which is in threaded engagement with a male screw 17 of a driven shaft 16. A pinion 21 formed at the end portion of the driven shaft 16 is meshed with a ring gear 22 which is secured to the sheave 4 by means of bolts 28. A flange portion 23 is formed on the driven shaft 16 in a manner to oppose the brake wheel 19. Linings 24, 24 are provided on opposing surfaces of the flange portion 23 and the brake wheel 19. A brake disk 26 which can rotate in one direction only through the frame 1 and a ratchet 25 is provided between the flange portion 23 and the brake wheel 19.
When it is desired to elevate the rope traction device by rotating the sheave 4 clockwise as viewed in FIG. 4, the driven shaft 16 is rotated counterclockwise. Since the ratchet 25 is free in this direction, the brake wheel 19 whose female screw 18 is in threaded engagement with the male screw 17 of the driven shaft 16 is displaced to the left as viewed in FIG. 3 by the rotation of the brake wheel 19 to press the brake disk 26 against the flange portion 23. Thus, the brake wheel 19 is rotated integrally with the driven shaft 16 to transmit the drive force to the sheave 4.
When the sheave is rotated counterclockwise, i.e., a direction in which the rope traction device is lowered, the disk brake 26 is locked by the ratchet 25 and the sheave 4 itself is in a loaded state. By the rotation of the motor 3, the brake wheel 19 is rotated in a direction in which the brake wheel 19 is displaced to the right as viewed in FIG. 3 and the rope traction device is lowered due to the load applied to the sheave 4 by a distance corresponding to the gap produced in the disk brake 26. The rope traction device is lowered by repeating release and engagement of the brake 7.
In the traction mechanism 6 described in which the rope 5 is pressed against the sheave 4 by the pair of rollers 10, 10 mounted on the pivoting arm 11, bending a moment is repeatedly applied to the rope 5 at points of contact with the V-shaped groove of the sheave 4 at two positions at which the rollers 10, 10 press the rope 5. Besides, the rollers 10, 10 tend to slip sideways by force applied in the transverse direction by twisting of the rope 5. For these reasons, wear occurs in the rope 5 and the life of the rope 5 thereby is shortened.
Besides, as wear occurs in the rope 5 and its diameter thereby is reduced, the position of the pivoting arm 8 before pivoting is changed so that the pressing force, i.e., traction force, obtained by inward displacement of the rollers 9, 9 is changed with resulting instability in the traction force.
It is, therefore, an object of the invention to provide a rope traction device which is capable of producing a large rope pressing force and ensuring a prolonged life of the rope without causing wear in it.
In the brake mechanism 7 in which the braking force is produced by the screw mechanism between the brake wheel 19 and the driven shaft 16, the force produced by the screws 17 and 18 is weak when the load is relatively small. This gives rise to the problem that, when grease used for lubricating the component parts such as wheels located near the linings 24, 24 contaminates the linings 24, 24, the force produced by the screws 17 and 18 is too small to force the grease out of the linings 24, 24 with a result that the braking force is decreased.
There is another problem in the brake mechanism 7 such that, when a large force such as an impact force has been applied to the brake mechanism 7, there is the likelihood that the tightening force produced between the screws 17 and 18 becomes excessively large with resulting malfunction of the brake 7.
In the brake mechanism 7 in which release and application of the brake 7 are repeated frequently during lowering of the rope traction device, grease tends to be deteriorated due to heat of friction produced in the linings 24, 24 when the distance of downward movement of the rope traction device is long with a result that the linings 24, 24 tend to burn and the braking efficiency is seriously reduced.
It is, therefore, another object of the invention to provide a rope traction device capable of producing a stable braking force regardless of the magnitude of load applied to the brake mechanism.